Name: 【TED-Ed】為什麼動物可以在黑暗中看得一清二楚?? (How do animals see in the dark? - Anna Stöckl)
Uploaded: 2016-09-22T21:59:59.000Z
Duration: 4 min 23 s

To human eyes, the world at night is a formless canvas of grey.

在人類的眼中，夜晚的世界籠罩在一層灰色無形的布幕之下

Many nocturnal animals, on the other hand,

experience a rich and varied world bursting with details, shapes, and colors.

能感受到一個充滿細節、形狀及色彩等豐富多樣的世界

What is it, then, that separates moths from men?

那麼到底是什麼區隔了蛾與人？

Moths and many other nocturnal animals see at night

蛾與其他許多夜行性動物有夜視力

because their eyes are adapted  to compensate for the lack of light.

是因為牠們的眼睛可以去彌補光線不足的情形

所有眼睛，不管是不是夜行性動物的，

depend on photoreceptors in the retina to detect light particles,

依賴視網膜上的感光細胞去偵測光粒子

Photoreceptors then report information about these photons to other cells

感光細胞接著會將這些光子的資訊傳給其他

The brain sifts through that information and uses it to build up an image

腦會篩選資訊並利用它來形成一個

The brighter the light is, the more photons hit the eye.

光線越亮，越多光子打進眼睛裡

upwards of 100 million times  more photons are available to the eye

比起一個陰天、沒有月亮的夜晚

Photons aren't just less numerous  in darkness,

光子在黑暗中不只是數量比較少

but they also hit the eye  in a less reliable way.

且它們以較不準確的方式打進眼睛中

This means the information  that photoreceptors collect

意思就是感光細胞所收集的資訊

In darkness, trying to detect the sparse scattering of randomly arriving photons

在黑暗中，試著去偵測稀疏散落且隨機分布的光子

is too difficult for the eyes of most daytime animals.

對許多日行性動物來說太困難了

But for night creatures,  it's just a matter of adaptation.

但是對夜間動物來說，這只是適應上的問題

Take the tarsier, whose eyeballs are each as big as its brain,

舉每顆眼球都和腦袋一樣大的跗猴為例，

giving it the biggest eyes compared  to head size of all mammals.

和頭相比牠可說是所有哺乳類中擁有最大的眼睛

If humans had the same brain to eye ratio, our eyes would be the size of grapefruits.

如果人類也擁有相同的腦-眼比例，我們的眼睛會和柚子一樣大

The tarsier's enlarged orbs haven't  evolved to make it cuter, however,

然而，跗猴的大眼球並沒有讓牠看起來比較可愛

Bigger eyes can have larger openings, called pupils,

比較大的眼睛就會有比較大的開口，也就是瞳孔

allowing for more light to be focused on the receptors.

可以讓更多的光線聚集在感覺器官上

While tarsiers scan the nocturnal scene with their enormous peepers,

當跗猴用牠們巨大的眼睛掃過夜景

貓用閃閃發光的眼來做同樣的事情

Cats' eyes get their shine from a structure called the tapetum lucidum

貓的眼睛從一個稱為脈絡膜層的構造來發亮

This structure is made from layers of mirror-like cells containing crystals

這構造是由層層包含水晶的鏡狀細胞所組成

that send incoming light bouncing back towards the photoreceptors

水晶會反彈進去的光線回到感光細胞

and it also gives the photoreceptors a second chance to detect photons.

且這讓感光細胞有第二次偵測光子的機會

In fact, this system has inspired the artificial cats' eyes we use on our roads.

事實上，這系統給我們製造出在路上所用的人工貓眼的靈感

Toads, on the other hand, have adapted to take it slow.

蟾蜍，另一方面，適應去慢慢來

even when just a single photon  hits each photoreceptor per second.

甚至在每秒每個感光細胞只能收到一個光子的情況下

that are more than 25 times slower  than human ones.

This means toads can collect photons for up to four seconds,

這代表蟾蜍可以收集四秒鐘的光子

allowing them to gather many more than our eyes do

讓牠們能夠聚集到比我們眼睛能夠做到的更多的光子

The downside is that this causes toads to react very slowly

because they're only receiving an updated image every four seconds.

因為牠們只能每四秒接收到一個更新的影像

Fortunately, they're accustomed to targeting sluggish prey.

幸虧牠們習慣獵捕行為緩慢的獵物

Meanwhile, the night is also buzzing with insects,

同時，夜晚也充滿著嗡嗡的昆蟲

which can see their favorite flowers in color, even on a starlit night.

鷹蛾可以看見牠們最愛的花的顏色，甚至在星光燦爛的夜晚

牠們利用一個令人驚訝的行為來做到這事：

getting rid of details  in their visual perception.

Information from neighboring photoreceptors is grouped in their brains,

在鄰近的感光細胞收到的資訊會在腦中成群

so the photon catch of each group is higher

However, grouping photoreceptors loses details in the image,

然而，群聚的感光細胞的影像會失去些細節

as fine details require a fine grid of photoreceptors,

因為完整的細節需要良好的感光細胞

each detecting photons from one small point in space.

每個細胞都能從一個小點的空間偵測到光子

The trick is to balance the need for photons with the loss of detail

這手段是以失去影像細節來平衡對光子的需求

Whether eyes are slow, enormous, shiny, or coarse,

不管是接收慢的、巨大的、亮晶晶的、或是粗糙的眼睛

it's the combination  of these biological adaptations

that gives nocturnal animals their unique visual powers.

讓夜行性動物擁有牠們獨特的視覺力量

Imagine what it might be like to witness through their eyes

想像一下從牠們的眼睛來觀看是什麼感覺

the world that wakes up when the sun goes down.

看這個當太陽下山才醒來的世界

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【TED-Ed】為什麼動物可以在黑暗中看得一清二楚?? (How do animals see in the dark? - Anna Stöckl)

brain

perceive

structure

world